Special Pdf
Clara Vanliere
An IPCC special report on the impacts of global warming of 1.5 C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. The translations of the SPM and other material can be downloaded from this link
Understanding the impacts of 1.5C global warming above pre-industrial levels and related global emission pathways in the context of strengthening the response to the threat of climate change, sustainable development and efforts to eradicate poverty.
This chapter frames the context, knowledge-base and assessment approaches used to understand the impacts of 1.5C global warming above pre-industrial levels and related global greenhouse gas emission pathways, building on the IPCC Fifth Assessment Report (AR5), in the context of strengthening the global response to the threat of climate change, sustainable development and efforts to eradicate poverty.
Past emissions alone are unlikely to raise global-mean temperature to 1.5C above pre-industrial levels (medium confidence), but past emissions do commit to other changes, such as further sea level rise (high confidence). If all anthropogenic emissions (including aerosol-related) were reduced to zero immediately, any further warming beyond the 1C already experienced would likely be less than 0.5C over the next two to three decades (high confidence), and likely less than 0.5C on a century time scale (medium confidence), due to the opposing effects of different climate processes and drivers. A warming greater than 1.5C is therefore not geophysically unavoidable: whether it will occur depends on future rates of emission reductions. 1.2.3, 1.2.4
1.5C emission pathways are defined as those that, given current knowledge of the climate response, provide a one- in-two to two-in-three chance of warming either remaining below 1.5C or returning to 1.5C by around 2100 following an overshoot. Overshoot pathways are characterized by the peak magnitude of the overshoot, which may have implications for impacts. All 1.5C pathways involve limiting cumulative emissions of long-lived greenhouse gases, including carbon dioxide and nitrous oxide, and substantial reductions in other climate forcers (high confidence). Limiting cumulative emissions requires either reducing net global emissions of long-lived greenhouse gases to zero before the cumulative limit is reached, or net negative global emissions (anthropogenic removals) after the limit is exceeded. 1.2.3, 1.2.4, Cross-Chapter Boxes 1 and 2
This report assesses projected impacts at a global average warming of 1.5C and higher levels of warming. Global warming of 1.5C is associated with global average surface temperatures fluctuating naturally on either side of 1.5C, together with warming substantially greater than 1.5C in many regions and seasons (high confidence), all of which must be considered in the assessment of impacts. Impacts at 1.5C of warming also depend on the emission pathway to 1.5C. Very different impacts result from pathways that remain below 1.5C versus pathways that return to 1.5C after a substantial overshoot, and when temperatures stabilize at 1.5C versus a transient warming past 1.5C (medium confidence). 1.2.3, 1.3
Ethical considerations, and the principle of equity in particular, are central to this report, recognizing that many of the impacts of warming up to and beyond 1.5C, and some potential impacts of mitigation actions required to limit warming to 1.5C, fall disproportionately on the poor and vulnerable (high confidence). Equity has procedural and distributive dimensions and requires fairness in burden sharing both between generations and between and within nations. In framing the objective of holding the increase in the global average temperature rise to well below 2C above pre-industrial levels, and to pursue efforts to limit warming to 1.5C, the Paris Agreement associates the principle of equity with the broader goals of poverty eradication and sustainable development, recognising that effective responses to climate change require a global collective effort that may be guided by the 2015 United Nations Sustainable Development Goals. 1.1.1
Climate adaptation refers to the actions taken to manage impacts of climate change by reducing vulnerability and exposure to its harmful effects and exploiting any potential benefits. Adaptation takes place at international, national and local levels. Subnational jurisdictions and entities, including urban and rural municipalities, are key to developing and reinforcing measures for reducing weather- and climate-related risks. Adaptation implementation faces several barriers including lack of up-to-date and locally relevant information, lack of finance and technology, social values and attitudes, and institutional constraints (high confidence). Adaptation is more likely to contribute to sustainable development when policies align with mitigation and poverty eradication goals (medium confidence). 1.1, 1.4
Multiple forms of knowledge, including scientific evidence, narrative scenarios and prospective pathways, inform the understanding of 1.5C. This report is informed by traditional evidence of the physical climate system and associated impacts and vulnerabilities of climate change, together with knowledge drawn from the perceptions of risk and the experiences of climate impacts and governance systems. Scenarios and pathways are used to explore conditions enabling goal-oriented futures while recognizing the significance of ethical considerations, the principle of equity, and the societal transformation needed. 1.2.3, 1.5.2
This chapter assesses mitigation pathways consistent with limiting warming to 1.5C above pre-industrial levels. In doing so, it explores the following key questions: What role do CO2 and non-CO2 emissions play? 2.2, 2.3, 2.4, 2.6 To what extent do 1.5C pathways involve overshooting and returning below 1.5C during the 21st century? 2.2, 2.3 What are the implications for transitions in energy, land use and sustainable development? 2.3, 2.4, 2.5 How do policy frameworks affect the ability to limit warming to 1.5C? 2.3, 2.5 What are the associated knowledge gaps? 2.6
The assessed pathways describe integrated, quantitative evolutions of all emissions over the 21st century associated with global energy and land use and the world economy. The assessment is contingent upon available integrated assessment literature and model assumptions, and is complemented by other studies with different scope, for example, those focusing on individual sectors. In recent years, integrated mitigation studies have improved the characterizations of mitigation pathways. However, limitations remain, as climate damages, avoided impacts, or societal co-benefits of the modelled transformations remain largely unaccounted for, while concurrent rapid technological changes, behavioural aspects, and uncertainties about input data present continuous challenges. (high confidence) 2.1.3, 2.3, 2.5.1, 2.6, Technical Annex 2
Pathways consistent with 1.5C of warming above pre-industrial levels can be identified under a range of assumptions about economic growth, technology developments and lifestyles. However, lack of global cooperation, lack of governance of the required energy and land transformation, and increases in resource-intensive consumption are key impediments to achieving 1.5C pathways. Governance challenges have been related to scenarios with high inequality and high population growth in the 1.5C pathway literature. 2.3.1, 2.3.2, 2.5
Under emissions in line with current pledges under the Paris Agreement (known as Nationally Determined Contributions, or NDCs), global warming is expected to surpass 1.5C above pre-industrial levels, even if these pledges are supplemented with very challenging increases in the scale and ambition of mitigation after 2030 (high confidence). This increased action would need to achieve net zero CO2 emissions in less than 15 years. Even if this is achieved, temperatures would only be expected to remain below the 1.5C threshold if the actual geophysical response ends up being towards the low end of the currently estimated uncertainty range. Transition challenges as well as identified trade-offs can be reduced if global emissions peak before 2030 and marked emissions reductions compared to today are already achieved by 2030 2.2, 2.3.5, Cross-Chapter Box 11 in Chapter 4.
Limiting warming to 1.5C implies reaching net zero CO2 emissions globally around 2050 and concurrent deep reductions in emissions of non-CO2 forcers, particularly methane (high confidence). Such mitigation pathways are characterized by energy-demand reductions, decarbonization of electricity and other fuels, electrification of energy end use, deep reductions in agricultural emissions, and some form of CDR with carbon storage on land or sequestration in geological reservoirs. Low energy demand and low demand for land- and GHG-intensive consumption goods facilitate limiting warming to as close as possible to 1.5C. 2.2.2, 2.3.1, 2.3.5, 2.5.1, Cross-Chapter Box 9 in Chapter 4.
In comparison to a 2C limit, the transformations required to limit warming to 1.5C are qualitatively similar but more pronounced and rapid over the next decades (high confidence). 1.5C implies very ambitious, internationally cooperative policy environments that transform both supply and demand (high confidence). 2.3, 2.4, 2.5
Limiting warming to 1.5C requires a marked shift in investment patterns (medium confidence). Additional annual average energy-related investments for the period 2016 to 2050 in pathways limiting warming to 1.5C compared to pathways without new climate policies beyond those in place today (i.e., baseline) are estimated to be around 830 billion USD2010 (range of 150 billion to 1700 billion USD2010 across six models). Total energy-related investments increase by about 12% (range of 3% to 24%) in 1.5C pathways relative to 2C pathways. Average annual investment in low-carbon energy technologies and energy efficiency are upscaled by roughly a factor of six (range of factor of 4 to 10) by 2050 compared to 2015, overtaking fossil investments globally by around 2025 (medium confidence). Uncertainties and strategic mitigation portfolio choices affect the magnitude and focus of required investments. 2.5.2
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